European patent publication 0,398,286 discloses a gas sensor for detecting ammonia. The gas sensor has an interdigitated electrode pair on a ceramic carrier and the gap between the electrodes is covered by a layer of polyaniline. The change of the electric resistance between the electrodes of the gas sensor is caused by the interaction of the ammonia with the polyaniline layer and is a measure of the ammonia concentration to be detected.
It is a disadvantage of this known gas sensor that it has insufficient long-term stability and that the indication provided thereby is not completely reversible.
Published German patent application 4,114,536 discloses special cage-like carbon molecule structures which can be characterized as so-called fullerenes. Fullerenes comprise a triple coordinated aromatic carbon with the molecules being composed exclusively of pentacycles and hexacycles, that is, the molecules have especially stable structures. All fullerenes contain twelve pentacycles and (n) hexacycles with (n) being an even number greater than or equal to zero. The number (x) of the carbon atoms of a fullerene molecule results from the number (n) of the hexacycles. The number (x) is given by: x=2 (n)+20. C.sub.60 fullerene and C.sub.70 fullerene should be mentioned in this context. The C.sub.60 fullerene has a precisely spherical-shaped structure with 20 hexagons on the surface and the C.sub.70 fullerene has 25 hexagons.
C.sub.60 and C.sub.70 fullerenes are significant for the practical application since they are especially simple to produce. For example, graphite is converted into C.sub.60 and C.sub.70 fullerenes to a certain proportion with a resistance heating in a helium atmosphere.
Detectable analytes can be organic analytes such as alkenes, alkynes and aromatic hydrocarbons or inorganic analytes such as ammonia, hydrazine, phosphine, H.sub.2 S and halogens.